Catecholamines and the sympathetic nervous system are important parts of the cardiovascular system in health and disease as well as in their interactions with pharmacological agents. The objective of this proposed study is to investigate the effect of chronic beta adrenergic blockade on catecholamine metabolism particularly as it relates to the propranolol withdrawal syndrome using an animal model and to study in human subjects with ischemic heart disease, changes in plasma catecholamines in response to reflex sympathetic stimulation. Guinea pigs given chronic doses of propranolol will be sacrificed and norepinephrine in their hearts and adrenal glands measured using a spectrofluorometric assay. The rate limiting enzyme in catecholamine biosynthesis, tyrosine hydroxylase will also be measured using a radioenzymatic assay. These measurements will be taken during chronic treatment and at various periods after withdrawal while cardiac propranolol levels are monitored using a spectrofluorometric assay. In the clinical study, patients with stable chest pain syndromes will be subject to the cold pressor test at the time of cardiac catheterization with monitoring of arterial blood pressure and the electrocardiogram. Blood for plasma dopamine-beta-hydroxylase and catecholamines will be taken from the coronary sinus and peripheral vein before and after the cold pressor test and levels measured using radioenzymatic assays. The responses will be compared in the patients who have significant disease of the left coronary artery with those who do not. It is felt that this study could better define the role of the sympathetic nervous system in ischemic heart disease and may demonstrate provocable biochemical markers for this entity.